Very little research has been conducted on marijuana in the past 25 years. The AMA is urging federal funding of research to determine the validity of marijuana as an effective medical treatment and to further evaluate the abuse potential of this drug. Marinol (dronabinol) is a synthetic orally active cannabinoid with few/no mind-altering properties and limited abuse potential, prescribed for clinicaL use in AIDS and chemotherapy patients in order to reduce nausea and/or stimulate appetite. This project is based on the hypothesis that Marinol will provoke similar cerebral blood flow changes, assessed via Oxygen (015) Water PET, to those observed by other researchers after their subjects were administered THC via injection or by smoking marijuana, although Marinol will not cause intoxication ('high'). Subjects are assessed blind to dose, on 2 doses of Marinol and placebo. Data will be analyzed when the subject N is sufficiently large.